I'm about 99% positive it was just left on. You can helicopter a dog with a prong collar on and not get it embedded like that. Put it on tight and snug and go 4 days without taking it off though and that's what you get. You can get that kind of thing with e collars too if you put it on snug and don't rotate the collar often enough. It eventually rubs it's way in. Kind of like how people get bedsores in hospitals.